With regard to the manufacture of N-monosubstituted (meth)acrylamides, a method involving reacting (meth)acrylic acid chloride with a primary amine in a neutralizing agent such as sodium hydroxide has been known. However, it is unlikely that said method is industrially advantageous because of the use of expensive materials and neutralizing agents and also the complexity of the operation. On the other hand, in accordance with the reaction of (meth)acrylates with an amines for manufacturing (meth)acrylamides, it is possible to use less expensive materials and, therefore, several methods for the manufacture of N-substituted (meth)acrylamides by said reaction have been known. Since the double bond in the (meth)acrylates is very reactive, the common means for the manufacture of the desired products in that case is that a protecting group such as an amine, cyclopentadiene, an alcohol, etc. is initially added to the double bond and, after completion of the amidation, the protecting group is detached by heating. For example, the use of cyclopentadiene as a protecting group is disclosed in Examined Japanese Patent Publication (Kokoku) Sho-54/9170, etc. while the use of alcohols as a protective group is disclosed in U.S. Pat. No. 3,914,303, etc.
Further, an example of the use of amines as a protecting group can be found in U.S. Pat. No. 2,451,436 disclosing a method in which an acrylate is made to react with a mono- or dialkylamine and the resulting N-alkyl-beta-alkylaminopropionamide is subjected to thermal decomposition in the presence of an acid to give an N-alkylacrylamide. Another example is Laid-Open Japanese Patent Publication (Koukai) Hei-04/154749 disclosing a method in which N-dimethylamino-beta-dimethylaminopropionamide is subjected to thermal decomposition in a liquid phase to give dimethylacrylamide at a good yield.
In the manufacture of N-substituted (meth)acrylamides using a (meth)acrylate as a starting material, the method using an amine as a protecting group may be industrially advantageous as compared with a method using an alcohol or cyclopentadiene because thermal decomposition in a liquid phase especially at a relatively low temperature is possible. However, though said method has a high yield and is industrially advantageous in the case of the manufacture of N,N-dialkyl(meth)acrylamides, there is a big disadvantage when applying it to the manufacture of N-monosubstituted (meth)acrylamides.
The disadvantage is that the N-monosubstituted beta-amino(methyl)propionamides prepared by the reaction of (meth)acrylates with a primary amine are accompanied by a large amount of impurities having high boiling points and high viscosities which both decrease the yield of the product. In addition, when it is subjected to thermal decomposition to give the desired substance, the boiling point (reaction temperature) becomes higher due to the presence of such highly viscous impurities with high-boiling-points whereby the polymerization of the desired substance is quite apt to take place in such a way so as to result in a further decrease in the yield which, in turn, raises the cost for the purification. In an extreme case, the operation becomes difficult and the expected product cannot be produced.